Chemical storage facilities located near population centers have long posed both a security and an emergency response challenge for government agencies. An accidental release of chemicals from a storage facility or a chemical transportation vehicle would require nearby municipal agencies to track the chemical's gas cloud or "plume" in order to determine its potential impact on nearby population centers. In light of the events of September 11, 2001, the possibility of an intentional release, with potentially high impact, must also be considered.

This article discusses a pilot application developed jointly by Erie County and Esri business partner URS Corporation's Buffalo, New York, office. This pilot application integrates the Environmental Protection Agency (EPA) Aerial Locations of Hazardous Atmospheres (ALOHA) program with MapObjects and ArcView technologies to provide rapid, real-time modeling and reporting for chemical plumes and the areas that they affect.

Erie County is located in western New York State. Its population is 950,265 (Census 2000) within a land area of 1,044 square miles. The county's largest city and county seat is Buffalo.

ALOHA is a program developed by the EPA Chemical Emergency Preparedness and Prevention Office (CEPPO) and the National Oceanic and Atmospheric Administration (NOAA) Office of Response and Restoration and is part of the agency's Computer-Aided Management of Emergency Operations (CAMEO) suite. It is available without cost. ALOHA contains a database of approximately 1,000 common chemicals. Using information from this database, including chemical type, accident location (urban or rural), weather conditions (temperature, wind speed, and wind direction), and accident parameters (storage medium, size of opening, pressure of storage medium), ALOHA can predict the atmospheric dispersion rate and direction of vapors from a broken pipe, tank, or other source. ALOHA can also generate a visual representation of the plume created by the chemical release.

ALOHA, designed as a lightweight emergency response tool and training aid, is relatively easy to use and integrates well with the CAMEO suite; the original CAMEO applications; and MARPLOT, a mapping application. ALOHA's limitations include reduced prediction capability at low wind speeds, with variable wind direction, or under highly unstable atmospheric conditions. ALOHA cannot incorporate chemical solutions, particulates, chemical reactions, or the results of fires into its modeling processes.

Prior to requesting assistance of URS, the Erie County GIS Division had experimented with an ArcView extension that converted and imported ALOHA plume geometry into ArcView 3. Use of the ArcView extension, however, required the operator to have some basic GIS experience. Moreover, the shapefile created by the extension could be created only in a decimal degrees coordinate system. Finally, the extension offered no analytical capabilities for determining which entities would be affected by the plume.

The county therefore began looking for a system that

• Required minimal to no GIS experience to use. It would thus be possible for emergency response personnel, not just county GIS staff, to run the application.
• Could automatically overlay and project the shapefile created from plume geometry developed by ALOHA into an ArcView view that would allow the operator to focus on the task at hand.
• Could run an analysis of county-defined geographic entities that might be affected by the plume.
• Would quickly create a report on the affected entities, covering county-defined attributes (such as population) to help quantify the effects. This report would contain an executive summary of potential plume effects for submittal to decision makers and a more detailed report.
• Utilized an autosave feature that would catalog and save each plume generation instance and allow the user to easily regenerate plume shapefiles and output summary reports and adjust emergency response planning and resources in response to changing atmospheric conditions.

A key benefit of the application is that it allows county GIS administrators to configure the application to present features from spatial data sources that emergency response decision makers would want to see in the event of an emergency. Examples of these data sources include schools, medical facilities, shelters, police and fire stations, and senior housing.

The Output Summary Report (OSR) created by the application was developed to provide maximum flexibility in reporting. An administrator of the application can determine which shapefiles will be overlaid against the plume shapefile.

In turn, specific attribute fields in a selected shapefile can be selected for inclusion in the OSR. If an attribute field contains numeric values, these can be summarized in the Executive Summary report. The order in which shapefiles are presented in the report can also be set in addition to the order of display for selected attribute fields from a shapefile.

County GIS administrators can also set the projection into which the plume will be projected after it has been imported into ArcView. For Erie County, this would typically be New York State Plane West North American Datum of 1983 (NAD 83), but options are also available for New York State Plane West NAD 27 and Universal Transverse Mercator (UTM) coordinate systems.